A wide variety of surgical procedures used today involve surgical instrumentation having jaw structure such as grippers, graspers, dissectors, clamps, cutting elements and/or stapling elements. In each of these types of jaw structure, selected tissue is captured by the jaws for manipulation. One type of jaw structure currently used captures tissue by a pivotal action of the jaw structure wherein the jaws close progressively from a pivot point outward to the end of the jaw structure. See, for example, U.S. Pat. No. 5,040,715 to Green et al. This pivotal action, however, causes the captured tissue to be pushed away from the jaw pivot point upon approximation, possibly resulting in uneven cutting, unintentional tissue trauma, and/or inaccurate tissue measurement or joining. This type of jaw structure is also disadvantageous in endoscopic or laparoscopic procedures wherein the surgical instrument is inserted into the body through a cannula or trocar because the jaws must necessarily protrude a significant distance beyond the end of the trocar to open fully. This decreases the “maneuver room” available to a surgeon for manipulating the device within a body cavity.
A more accurate and atraumatic way of approximating surgical jaw structure is by parallel approximation. This approach has been described in European Patent Application No. 92104388.1, filed Mar. 13, 1992, wherein various canning structures are described for effecting substantially parallel movement of first and second surgical jaws. In one embodiment, a camming plate with diagonal canning slots is slidably mounted within a tubular frame. The canning plate is connected to a movable jaw such that movement of the camming plate causes the movable jaw to move into parallel approximation with a stationary jaw. In another embodiment, an axially slidable camming collar engages a camming surface on the movable jaw to actuate the opening and closing of the jaws. Sliding the collar forward closes the jaws, whereas pulling the collar backward opens the jaws. This design, however, creates a very high frictional component to the overall opening and closing forces, affecting the overall ease of operation of the device. Additionally, in all of the embodiments described, the jaws are prevented from moving axially, which, as will be discussed below, precludes the user from enjoying many other advantages.
The above devices also describe jaw structures that employ a staple cartridge. Typically, the staple cartridge is provided with an axially extending slit through which a knife passes to cut the captured tissue at the time of stapling. An axially movable actuating mechanism (e.g., a pusher rod) is used to push the knife through the cartridge. The location and structure of the knife actuating mechanism is well known for jaws having purely pivotal movement, but such is not the case for jaws that are capable of substantially parallel approximation. In this latter situation, especially in connection with endoscopic or laparoscopic procedures where accessibility is extremely limited, inclusion of the knife actuating mechanism can result in a reduction in the maximum distance the jaws can open and/or result in further penetration of the jaws beyond the end of the cannula into the body cavity to accommodate the knife actuating mechanism.
It is also desirable to have a fresh knife available after each transection. In presently available apparatus, however, the knife has been an integral part of the combined pusher rod/cartridge assembly. This design requires the pusher rod mechanism to be discarded after each use, causing waste, and requires that the overall length of the cartridge assembly be increased in size to account for the entire extended length of the pusher rod mechanism.
Another disadvantage of the above-described devices is that jaw closing is typically accomplished by actuating an axially movable rod operably connected to the jaws. Pushing on the actuating rod closes the jaws and pulling on it opens them. Using compression force on the actuating rod, however, to close the jaws around the captured tissue can result in buckling. This could have serious consequences if buckling occurred during a particularly sensitive part of the surgical procedure.
In view of the above, it should be appreciated that there is still a need for a jaw-type surgical instrument wherein the jaws are held substantially parallel over a significant part of their operating range, yet open widely with minimal extension of the jaws beyond the end of the cannula into the body cavity during the operating procedure. There is also a need for a device wherein the jaws are axially movable to effect approximation and wherein the mechanism for closing the jaws around the captured tissue is without risk of instrument failure due to buckling of the push rod. Such a device would also preferably include an easily replaceable knife without significantly affecting the operation of the jaws or requiring frequent replacement of the knife actuating mechanism. The present invention satisfies these needs.